Investigation of extended-spectrum beta-lactamases produced by clinical isolates of Klebsiella pneumoniae and Escherichia coli in Korea

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Abstract
Aims: Isolates obtained from various regions in Korea in 2002 were identified and their susceptibility to extended‐spectrum cephalosporins, monobactams and/or cephamycins was studied along with any production of extended‐spectrum β‐lactamases (ESBLs). Methods and Results: Bacteria identified by the conventional techniques and Vitek GNI card were Klebsiella pneumoniae and Escherichia coli. Using disk diffusion and double‐disk synergy tests, we found that 39·2% of strains produced ESBLs. About 52% of isolates transferred resistance to ceftazidime by conjugation. Banding patterns of PCR amplification with the designed primers showed that 837‐ and 259‐bp fragments specific to blaTEM genes were amplified in 63·3% of strains. 929‐ and 231‐bp fragments (blaSHV), 847‐ and 520‐bp fragments (blaCMY), 597‐ and 858‐bp fragments (blaCTX‐M) were amplified in 61·5, 17·3 and 7·7% of strains respectively. About 51·9% of strains contained more than two types of β‐lactamase genes. Especially, one strain contained blaTEM, blaCMY and blaCTX‐M genes. Significance: Resistance mechanisms to β‐lactams, comprising mostly ESBL production, lead to the resistance against even recently developed β‐lactams in enterobacteria, which is now a serious threat to antibiotic therapy. The high prevalence of blaCMY genes and multidrug‐resistant genes may also make therapeutic failure and lack of eradiation of these strains by extended‐spectrum cephalosporins or cephamycins.

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